It is well known that limiting the exposure of an oxygen sensitive product to oxygen maintains and enhances the quality and shelf life of the product. For instance, by limiting the oxygen exposure of an oxygen sensitive food product in a packaging system, the quality of the food product is maintained by minimizing nutrient loss, slowing enzymatic and lipolytic oxidation, preventing photolytic degradation, and reducing spoilage. In addition, such packaging also keeps the product in inventory longer, thereby reducing restocking costs, and costs incurred from waste.
One means for limiting the exposure of a product to oxygen involves incorporating an oxygen scavenger into the packaging structure itself. This achieves a more uniform scavenging effect throughout the package. This may be especially important where there is restricted air circulation inside the package. In addition, such incorporation can provide a means of intercepting and scavenging oxygen as it passes through the walls of the package (herein referred to as an "active oxygen barrier"), thereby maintaining the lowest possible oxygen level throughout the package.
Oxygen scavengers that can be incorporated into a film structure are disclosed in U.S. Pat. Nos. 5,310,497, 5,350,622 and 5,399,289 (Speer et al.), and a method of initiating oxygen scavenging generally is disclosed in U.S. Pat. No. 5,211,875 (Speer et al.). All of these four patents are incorporated herein by reference in their entirety. According to U.S. Pat. No. 5,350,622, oxygen scavengers are made of an ethylenically unsaturated hydrocarbon and transition metal catalyst. The preferred ethylenically unsaturated hydrocarbon may be either substituted or unsubstituted. The "oxygen scavenger" materials disclosed by Speer et al. are compounds which consume, deplete or reduce the amount of oxygen from a given environment.
Other oxygen scavengers which can be incorporated into a film structure are disclosed in PCT patent publication WO 94/12590 (Commonwealth Scientific and Industrial Research Organisation). These oxygen scavengers include at least one reducible organic compound which is reduced under predetermined conditions, the reduced form of the compound being oxidizable by molecular oxygen, wherein the reduction and/or subsequent oxidation of the organic compound occurs independent of the presence of a transition metal catalyst. The reducible organic compound is preferably a quinone, a photoreducible dye, or a carbonyl compound which has absorbence in the UV spectrum.
Oxygen scavengers are useful in MAP (modified atmosphere packaging) and barrier packaging environments. However, oxygen scavengers often require, or at least benefit from, triggering in order to activate the oxygen scavenging properties.
In copending U.S. patent application Ser. No. 08/691,829 filed Aug. 2, 1996, incorporated by reference herein in its entirety, an apparatus is disclosed which is beneficial in triggering oxygen scavenger films. This apparatus is especially useful when employed in a food processing plant or other facility where the triggering apparatus is located near a packaging machine. Thus disposed, an oxygen scavenger film can be triggered shortly before, and perhaps just a few seconds before, the film is used to package a food or other oxygen sensitive product.
Although these technologies offers great potential in packaging applications, it has been found that oxygen scavenger structures can sometimes generate reaction by-products which can adversely affect the taste and/or smell of the packaged material (i.e. organoleptic properties). These by-products can include acids, alcohols, alkenes, dienes, esters, aldehydes and ketones.
Technical solutions to this problem are disclosed in WO 97/32924 and WO 97/32925, both published Sep. 12, 1997 and both incorporated by reference herein in their entirety. These publications disclose various functional barrier materials suitable for use in multilayer oxygen scavenger films. These functional materials lower the amount of extractables, such as aldehydes, and the degree of undesirable organoleptic transfer, resulting from absorption of low molecular weight by-products of an oxygen scavenging reaction.
The inventors have found that although these technical solutions offer beneficial improvements in reducing extractables of organoleptic off-odors and off-flavors in oxygen scavenging films, still further improvement would be beneficial. It is now believed that in oxygen scavenger systems as described herein, the production of extractables is driven by two events.
The first event is the incidence of actinic radiation, e.g. ultraviolet light, onto the oxygen scavenger film, as occurs in the chamber of a triggering unit of the types described herein and in U.S. patent application Ser. No. 08/691,829. This procedure is known as "triggering" the film, leading to activation (usually within a short time) of the oxygen scavenger in the film. Unfortunately, this process is believed to also result in the photolytic degradation or breakdown of material in the film, e.g. at the film surface, and the production, as a by-product of this process, of organic materials such as aldehydes, ketones, etc.
The second event is the time at which the now triggered film actually activates, i.e. begins to scavenge oxygen. At this stage, the oxidizable organic compound present in the film or other article begins to oxidize, producing additional organic materials (aldehydes, ketones, etc.) as a by-product of the oxygen scavenging reaction.
The elapsed time between these two events is known as the induction time or induction period of the article.
In some cases, an article such as a film may not be exposed to actinic radiation, yet contain organic compounds which can adversely affect the organoleptic properties of a product to be contained in, or packaged with, the article.
The inventors have found that the benefits of lowered extractables and enhanced, i.e. improved, organoleptic properties can be obtained by treating an article at the same time as, and/or after, the article has been exposed to actinic radiation, e.g. UV light, preferably soon after this event, and more preferably during the induction period. The invention provides an effective method of and apparatus for lowering the amount of the extractables of a triggered article comprising an oxidizable organic compound, compared with a method and apparatus without the benefit of the invention.
The method and apparatus preferably provide that the article is treated prior to, and more preferably immediately prior to packaging of an oxygen sensitive product with the article.
Preferably, the invention provides a spatially compact-treating means.
Preferably, an apparatus is provided which is readily incorporated in-line into existing packaging systems.
In some cases, an oxygen scavenger article may not require exposure to actinic radiation in order to activate the scavenging functionality of the article. Nevertheless, organic products may be present, and/or generated by the oxygen scavenging process, and these products can sometimes adversely affect the organoleptic properties of a product to be contained in, or packaged with, the article. The invention can also be beneficial in lowering the amount of such organic compounds in such systems.
In still other cases, an article such as a film can contain organoleptic compounds as defined herein, even though the article does not contain an oxidizable organic compound. Here, too, the invention can be beneficially used to lower the amount of such organoleptic compounds in the article.